A conventional controller having a servo amplifier built in a cabinet is shown in FIGS. 3 and 4.
A cabinet 1 of the controller is constituted by a rectangular box, and the inner space of the box is divided into forward and backward parts by a partition plate 2 arranged at the center of the inner space. A rectangular opening 5 is formed in the left-side portion of the partition plate 2. In addition, mounting bolts (not shown) are provided in a standing manner on a front surface of the partition plate 2 near four corners of the rectangular opening 5.
Bolt insertion holes 21 are formed at four corners of a rectangular base plate 6 in correspondence with the positions of the mounting bolts. A control unit 3 of a servo amplifier is fixed to the front surface of the base plate 6, and a heat-radiation unit (not shown) of the servo amplifier is fixed to the rear surface. The mounting bolts of the base plate 6 are inserted into the bolt insertion holes 21 of the base plate 6, and the tops of the mounting bolts are fastened by nuts 7. At this time, the base plate 6 is fixed to the partition plate 2 to close the opening 5.
A numeral control unit 4 is attached to a right-side portion on the front surface of the partition plate 2. Therefore, in a state where the base plate 6 having the control unit 3 of the servo amplifier attached to the front surface and the heat-radiation unit of the servo amplifier attached to the rear surface is fixed to the partition plate 2 through the mounting bolts and the nuts 7, the control unit 3 of the servo amplifier and the numeral control unit 4 are arranged in a forward space partitioned by the partition plate 2, and the heat-radiation unit of the servo amplifier is arranged in a backward space. An air-blowing fan (not shown) for exhausting air heated by heat radiated from the heat-radiation unit of the servo amplifier to the outside is arranged in the backward space.
The control unit 3 of the servo amplifier is connected to other electric parts, e.g., the numeral control unit 4, in the cabinet 1 through a direct-mounted cable 8 or a connector cable 9. A panel 10 for performing maintenance operations for the control unit 3 of the servo amplifier and the numeral control unit 4 is attached to the front surface of the cabinet 1 such that the panel 10 can be freely opened and closed.
Since a large number of electric parts which are expandable are mounted on the control unit 3 and the heat-radiation unit of the servo amplifier, maintenance operations for these parts must be performed. For this purpose, the control unit 3 and the heat-radiation unit of the servo amplifier must be detached out of the cabinet 1, however, when the conventional cabinet structure shown in FIG. 3, the opening/closing panel 10 is opened to take the cables 8 and 9 out, meshing of the nuts 7 for fixing the four corners of the base plate 6 is released, so that the control unit 3 and the heat-radiation unit of the servo amplifier are detached out of the cabinet 1 together with the base plate 6. Such cumbersome operations are required.